1. Field of the Invention
The present invention relates to a guide apparatus which is used in a linear guide section of, e.g., a machine tool or a like tool, for the purpose of guiding a movable member, such as a table, over a stationary section, such as a bed, and in which a slider equipped with a plurality of rolling elements, which elements circulate endlessly, freely travels back and forth along a track rail. More specifically, the present invention relates to an improvement for effecting high-speed movement of a slider on the raceway rail.
2. Description of the Related Art
As a guide apparatus of this type, there has hitherto been known a guide apparatus comprising a track rail which is disposed on a stationary section, such as a bed, and has a raceway surface for rolling members, such as rollers, formed therein; and a slider which is attached to the track rail by way of a plurality of rolling elements and travels along the track rail while supporting a movable element such as a table.
The slider has a load raceway surface opposing a raceway surface of a track rail via rolling elements, and a return path disposed parallel to the load raceway surface. Further, the slider comprises a slide block that is movable along the track rail in association with rolling action of the rolling elements, and a pair of end caps. The end caps are fixed to respective end faces of the slide blocks and have a U-shaped turning path (called a xe2x80x9cU-turn path). The U-turn path guides, toward the return path, rolling elements which have passed by a position between the load raceway surface of the slide block and the raceway surface of the track rail. The end caps are fixed to the respective end faces of the slide block, as a result of which the load raceway surface is connected to the end of the return path by way of the U-turn path. Thus, an endless circulation path is completed within the slider.
The rolling elements circulating through the endless circulation path of the slider roll through a position between the load raceway surface of the slide block and the raceway of the track rail. More specifically, the rolling elements roll through a load area while receiving the load exerted on the slide block. In a non-load area, the rolling elements are released from load and roll in a non-load state in which no load is exerted on the rolling elements. FIG. 7 is an enlarged cross-sectional view showing a junction between the non-load area and the load area. More specifically, the drawing shows that rolling elements 101 having rolled through a U-turn path 100 without receiving load enter a position between a raceway surface 103 of a track rail 102 and a load raceway 105 of a slide block 104. The load raceway surface 105 of the slide block 104 and the rolling elements 101, such as balls or rollers, are made of steel but are not completely rigid bodies and have slight elasticity. In the load area, the load raceway surface 105 and the rolling elements 101 are susceptible to slight elastic deformation due to load, and in the non-load area the rolling elements are restored to their original shapes upon being released from the load. For these reasons, the inner diameter of the return path and that of the U-turn path 100, which constitute the non-load area, are greater than the diameter of the rolling element 101. However, an interval between the load raceway surface 105 of the slide block 104 in the load area and the raceway surface 103 of the track rail 102 is smaller than the diameter of the rolling element 101. Hence, if the rolling elements 101 having rolled through the non-load area abruptly enter the load area, the rolling elements 101 are subjected to abrupt compression at the entrance of the load area. As a result, large resistance is imposed on circulation of the rolling elements 101, and noise associated with circulation of the rolling elements 101 becomes greater. For these reasons, in order to smoothly and resiliently deform the rolling elements 101 which enter the load area from the non-load area, each longitudinal end of the load raceway surface 105 has hitherto been subjected to crowning. Each end of the load area is slightly broadened, in the form of a bell bottom, toward the non-load area. By means of such broadening of the load area, the rolling elements 101 that have rolled into the load area from the non-load area roll to the depth of the load area, thereby diminishing circulation resistance and noise of the rolling elements 101.
As mentioned above, the U-turn path 100 constituting the non-load area is defined by the end cap 107 differing from the slide block 104 that has the load raceway surface 105 formed thereon. In order to effect smooth transfer of the rolling elements 101 between the non-load area and the load area, the end cap 107 must be positioned accurately in relation to the slide block 104. In the related art, an attempt has been made to increase positional accuracy in attaching the end cap 107 to the slide block 104, by means of fitting a boss projecting from the end cap 107 into a recessed hole formed in the end face of the slide block 104, thereby completely matching the edge of the crowned load raceway surface 105 to a sidewall surface 106 at the interior diameter of the U-turn path 100.
Even when positional accuracy in mounting the end cap 107 relative to the slide block 104 has been increased, the sidewall surface 106 at the interior diameter of the U-turn path 100 becomes lower than the edge of the load raceway surface 105, by virtue of the relationship between accuracy in formation of the load raceway surface 105 and accuracy in formation of the plastic end cap 107, as indicated by broken lines shown in FIG. 7. Eventually, there may arise a case where the edge of the load raceway surface 105 projects slightly at a junction between the load raceway surface 105 and the U-turn path 100. In this way, if the rolling elements 101 enter the load area from the U-turn path 100, the rolling elements 101 collide with the edge of the thus-projecting load raceway surface 105. Such a collision does not pose a serious problem when the slider travels along the track rail at a low speed; however, the collision poses a noticeable problem when there is a necessity of increasing the speed at which the slider is to travel along the track rail. Hence, if the speed at which the slider travels along the track rail is increased, within a given period of time a larger number of balls come to collision with the load raceway surface. As a result, resistance imposed on circulation of the rolling elements or noise becomes noticeable. Further, since impact energy is proportional to the square of speed, the edge of the projecting load raceway surface becomes vulnerable to damage.
A semi-circular guide section situated at the interior diameter of the U-turn path 100 has hitherto been attached to an end cap or a slide block. However, in order to increase an accuracy in formation of an endless circulation path, there has recently been practiced direct formation of the semi-circular guide section at the end face of the slide block by means of injection molding of synthetic resin (as described in Japanese Patent Application Laid-Open No. 317762/1995). Even in that case, difficulty is encountered in matching the edge of the load raceway surface to the inner side surface of the U-turn path having a semi-circular guide section provided thereon, without involvement of formation of a step. High-speed circulation of rolling elements has encountered the previous problems.
The present invention has been conceived in light of the drawbacks and aims at providing a linear guide apparatus which avoids occurrence of collision of rolling elements, which would otherwise arise when the rolling elements roll into a load area from a non-load area, thereby diminishing slide resistance and noise, which would otherwise arise when a slider moves at high speed relative to a track rail.
In order to achieve the object, ideally the load raceway surface completely matches and becomes continuous with the sidewall surface at the inner diameter of the U-turn path when the linear guide apparatus is assembled. However, preset tolerances are present in accuracy of formation of individual components or positioning accuracy. In order to realize an ideal match between the load raceway surface and the sidewall surface, a slider main body and end caps must be machined with a considerably high degree of accuracy and the thus-machined components must be assembled with a considerably high degree of precision. Therefore, difficulty is encountered in realizing such highly-accuracy machining and assembly of parts.
In the linear guide apparatus according to the present invention, the sidewall surface at the inner diameter of the U-turn path and the load raceway surface are not formed intentionally to become continuous in the location where the U-turn path is connected to the load raceway surface; rather, a step section is intentionally formed such that the edge of an entrance of the load raceway surface becomes higher than the sidewall surface.
By means of such technical means, the longitudinal edge of the load raceway surface is recessed in comparison with the sidewall surface at the inner diameter of the U-turn path. Hence, the rolling elements which attempt to enter a load area from the U-turn path do not collide with the edge of the load raceway surface, and the rolling elements can be smoothly delivered to the load area from the non-load area. Further, the U-turn path originally has an inner diameter greater than the diameter of the rolling element. Hence, even when the sidewall surface at the inner radius of the U-turn path protrudes beyond the edge of the entrance of the load raceway surface, the rolling elements which attempt to enter the U-turn path from the load are not caught by an angle of the sidewall surface. Hence, the rolling elements can be smoothly delivered to the non-load area from the load area.
The step section has a size of about 5% the diameter of the rolling element. The step section of such a size can be readily formed by means of adjusting a tolerance associated with formation of the load raceway surface or the end cap. Further, an allowable range is available for the size of the step section. Hence, formation of the step section is considerably easier than realization of complete match between the sidewall surface and the load raceway surface.
Even when it is impossible to realize a match between the load raceway surface and the sidewall surface at the inner diameter of the U-turn path by means of only setting an accuracy in formation of components or only assembly of accurate components, realization of a match between the load raceway surface and the sidewall surface can be implemented by means of machining the linear guide apparatus after assembly. More specifically, by means of simultaneously grinding the load raceway surface and the sidewall surface, which are adjacent to each other, a protuberance in the edge of the entrance of the load raceway surface relative to the sidewall surface is obviated, thereby finishing the surfaces so as to become continuous without a step. Thereby, there can be ensured ideal continuity between the load area and the non-load area with involvement of only a small amount of labor, thus realizing smooth circulation of rolling elements.
The present invention can be applied to an endless circulation path of a ball spline consisting of a spline shaft and a nut member to travel along the shaft, as well as to an endless ball circulation path of a linear guide apparatus consisting of a track rail and a slider.